This is Kant’s calculator for working out the rules of life
Create a Maxim (rule) that you can set yourself.
Act only according to that maxim whereby you can at the same time will that it should become a universal law (every one must follow it).
Act in such a way that you treat humanity, whether in your own person or in the person of any other, always at the same time as an end and never merely as a means to an end. (Always treat people as the goal and never a way to use to get to goal)
Therefore, every rational being must so act as if he or she were through his maxim always a legislating member in the universal kingdom of ends. (Everybody treats themselves as in a position to use this law)
Examples
Deception
Kant asserted that lying, or deception of any kind, would be forbidden under any interpretation and in any circumstance. In Grounding, Kant gives the example of a person who seeks to borrow money without intending to pay it back. This is a contradiction because if it were a universal action, no person would lend money anymore as he knows that he will never be paid back. The maxim of this action, says Kant, results in a contradiction in conceivability (and thus contradicts perfect duty). With lying, it would logically contradict the reliability of language. If it is universally acceptable to lie, then no one would believe anyone and all truths would be assumed to be lies. The right to deceive could also not be claimed because it would deny the status of the person deceived as an end in himself. And the theft would be incompatible with a possible kingdom of ends. Therefore, Kant denied the right to lie or deceive for any reason, regardless of context or anticipated consequences.
Theft
Kant argued that any action taken against another person to which he or she could not possibly consent is a violation of perfect duty interpreted through the second formulation. If a thief were to steal a book from an unknowing victim, it may have been that the victim would have agreed, had the thief simply asked. However, no person can consent to theft, because the presence of consent would mean that the transfer was not a theft. Since the victim could not have consented to the action, it could not be instituted as a universal law of nature, and theft contradicts perfect duty.
Charity
Kant's last application of the categorical imperative in Grounding for the Metaphysics of Morals is of charity. He proposes a fourth man who finds life fine but sees other people struggling with life. This man ponders about what if he did nothing to help those in need while not envying them or accepting anything from them. While Kant admits that humanity could subsist (and admits it could possibly perform better) if this was universal, he states in Grounding that: "But even though it is possible that a universal law of nature could subsist in accordance with that maxim, still it is impossible to will that such a principle should hold everywhere as a law of nature. For a will which resolved in this way would contradict itself, inasmuch as cases might often arise in which one would have need of the love and sympathy of others and in which he would deprive himself, by such a law of nature springing from his own will, of all hope of the aid he wants for himself."
Cruelty to Animals
Although actions with respect to non-rational agents do not have intrinsic moral content, Kant derived a prohibition against cruelty to animals as a violation of a duty in relation to oneself. According to Kant, man has the duty to strengthen the feeling of compassion, since this feeling promotes morality in relation to other human beings. But, cruelty to animals deadens the feeling of compassion in man. Therefore, man is obliged not to treat animals brutally (Kant, Metaphysics of Morals, § 17). However, Kant also argued that as animals are not rational beings and humans are, animals are only valued on how much they serve human purposes.
Suicide
Kant applied his categorical imperative to the issue of suicide in Grounding for the Metaphysics of Morals. writing that: "A man reduced to despair by a series of misfortunes feels sick of life, but is still so far in possession of his reason that he can ask himself whether taking his own life would not be contrary to his duty to himself. Now he asks whether the maxim of his action could become a universal law of nature. But his maxim is this: from self-love I make as my principle to shorten my life when its continued duration threatens more evil than it promises satisfaction. There only remains the question as to whether this principle of self-love can become a universal law of nature. One sees at once that a contradiction in a system of nature whose law would destroy life by means of the very same feeling that acts so as to stimulate the furtherance of life, and hence there could be no existence as a system of nature. Therefore, such a maxim cannot possibly hold as a universal law of nature and is, consequently, wholly opposed to the supreme principle of all duty." – Immanuel Kant, Grounding for the Metaphysics of Morals, p30-31
How Kant works out the rules of life
This is Kant’s calculator for working out the rules of life
Examples
Deception
Kant asserted that lying, or deception of any kind, would be forbidden under any interpretation and in any circumstance. In Grounding, Kant gives the example of a person who seeks to borrow money without intending to pay it back. This is a contradiction because if it were a universal action, no person would lend money anymore as he knows that he will never be paid back. The maxim of this action, says Kant, results in a contradiction in conceivability (and thus contradicts perfect duty). With lying, it would logically contradict the reliability of language. If it is universally acceptable to lie, then no one would believe anyone and all truths would be assumed to be lies. The right to deceive could also not be claimed because it would deny the status of the person deceived as an end in himself. And the theft would be incompatible with a possible kingdom of ends. Therefore, Kant denied the right to lie or deceive for any reason, regardless of context or anticipated consequences.Theft
Kant argued that any action taken against another person to which he or she could not possibly consent is a violation of perfect duty interpreted through the second formulation. If a thief were to steal a book from an unknowing victim, it may have been that the victim would have agreed, had the thief simply asked. However, no person can consent to theft, because the presence of consent would mean that the transfer was not a theft. Since the victim could not have consented to the action, it could not be instituted as a universal law of nature, and theft contradicts perfect duty.Charity
Kant's last application of the categorical imperative in Grounding for the Metaphysics of Morals is of charity. He proposes a fourth man who finds life fine but sees other people struggling with life. This man ponders about what if he did nothing to help those in need while not envying them or accepting anything from them. While Kant admits that humanity could subsist (and admits it could possibly perform better) if this was universal, he states in Grounding that:"But even though it is possible that a universal law of nature could subsist in accordance with that maxim, still it is impossible to will that such a principle should hold everywhere as a law of nature. For a will which resolved in this way would contradict itself, inasmuch as cases might often arise in which one would have need of the love and sympathy of others and in which he would deprive himself, by such a law of nature springing from his own will, of all hope of the aid he wants for himself."
Cruelty to Animals
Although actions with respect to non-rational agents do not have intrinsic moral content, Kant derived a prohibition against cruelty to animals as a violation of a duty in relation to oneself. According to Kant, man has the duty to strengthen the feeling of compassion, since this feeling promotes morality in relation to other human beings. But, cruelty to animals deadens the feeling of compassion in man. Therefore, man is obliged not to treat animals brutally (Kant, Metaphysics of Morals, § 17). However, Kant also argued that as animals are not rational beings and humans are, animals are only valued on how much they serve human purposes.Suicide
Kant applied his categorical imperative to the issue of suicide in Grounding for the Metaphysics of Morals. writing that:"A man reduced to despair by a series of misfortunes feels sick of life, but is still so far in possession of his reason that he can ask himself whether taking his own life would not be contrary to his duty to himself. Now he asks whether the maxim of his action could become a universal law of nature. But his maxim is this: from self-love I make as my principle to shorten my life when its continued duration threatens more evil than it promises satisfaction. There only remains the question as to whether this principle of self-love can become a universal law of nature. One sees at once that a contradiction in a system of nature whose law would destroy life by means of the very same feeling that acts so as to stimulate the furtherance of life, and hence there could be no existence as a system of nature. Therefore, such a maxim cannot possibly hold as a universal law of nature and is, consequently, wholly opposed to the supreme principle of all duty."
– Immanuel Kant, Grounding for the Metaphysics of Morals, p30-31